A fertilized mammalian egg autonomously develops into a blastocyst, which must be successfully implanted in the uterus. In higher primates including humans, trophectoderm cells at the embryonic pole adhere to the maternal epithelium (Hertig, A T, et al. 1956; Hertig, A T, et al. 1973; Padykula, H A. 1983; Enders, A C, et al. 1997). Apically-adhered trophectoderm cells rapidly grow and invade maternal tissue (Hertig, A T, et al. 1973; Knoth, M, et al. 1972; Enders, A C. 1976; Lindenberg, S, et al. 1986), suggesting that a mechanism triggered by adhesion stimulates silent trophectoderm to form an active trophoblast. Embryo implantation is unique to mammals; however, the process of implantation differs significantly among species (Carson, D D, et al. 2000). Some mechanisms underlying human embryo implantation are likely unique; for example, ectopic implantation is not rare in humans (Brenner, P F, et al. 1980), while it does not occur in other animals (Orsini, M W. et al. 1967).
Male infertility can result from a deficiency in sperm motility. In a normal human semen sample there are approximately 4-40×107 sperm, which upon ejaculation swim actively forward, cross through the uterine cervix to the opening of the fallopian tube, wherein about 250 sperm reach the fertilization site by chemotaxis. In the uterus, sperm become capacitated (i.e., capable to fertilize), acquire the ability to undergo the acrosome reaction (AR) and become hyperactivated. This hyperactivation is required for the sperm to penetrate the egg's extracellular matrix (zona pellucida). When sperm reach the isthmus in the oviduct female reproductive tract they slow down and resume their hyperactivated motility only after ovulation, probably due to the rise in progesterone and other yet undefined chemical attractants. The various cycles and forms of sperm motility occurring inside the female reproductive tract suggest that biochemical processes regulate each phase of the spermatozoa life cycle and that male fertility is partially dependent on factors present in the female genital tract. Thus, there is a widely recognized need for methods and compositions suitable for enhancing male fertility and promoting trophoblast formation.